3-D printed fluoropolymer structures

ABSTRACT

The invention relates to fluoropolymer filament for use in 3-D printing, and 3-D printed fluoropolymer articles having low warpage, excellent chemical resistance, excellent water resistance, flame resistance, and good mechanical integrity. Additionally, the articles of the invention have good shelf life without the need for special packaging. In particular, the invention relates to filament, 3-D printed polyvinylidene fluoride (PVDF) articles, and in particular material extrusion 3-D printing. The articles may be formed from PVDF homopolymers, copolymers, such as KYNAR® resins from Arkema, as well as polymer blends with appropriately defined low shear melt viscosity. The PVDF may optionally be a filled PVDF formulation. The physical properties of the 3-D printed articles can be maximized and warpage minimized by optimizing processing parameters.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. application Ser. No.15/635,525 filed Jun. 28, 2017, now U.S. Pat. No. 10,633,468, whichclaims the benefit of PCT Application PCT/US2017/025357, filed Mar. 31,2017, which claims the benefit of U.S. Provisional Application No. U.S.62/316,687, filed Apr. 1, 2016; and U.S. Provisional Application No.U.S. 62/320,649, filed Apr. 11, 2016, said applications incorporatedherein by reference.

FIELD OF THE INVENTION

The invention relates to fluoropolymer filament for use in 3-D printing,and 3-D printed fluoropolymer articles having low warpage, excellentchemical resistance, excellent water resistance, flame resistance, andgood mechanical integrity. Additionally, the articles of the inventionhave good shelf life without the need for special packaging. Inparticular, the invention relates to 3-D printed polyvinylidene fluoride(PVDF) articles, and in particular material extrusion 3-D printing. Thearticles may be formed from PVDF homopolymers, copolymers, and polymerblends with appropriately defined low shear melt viscosity. The PVDF mayoptionally be a filled PVDF formulation. The physical properties of the3-D printed articles can be maximized and warpage minimized byoptimizing processing parameters.

BACKGROUND OF THE INVENTION

Equipment advances and reduction in pricing have allowed 3D printing tobecome widely adopted in homes, schools, and industry as a fast,simpler, and often cheaper way to prototype and make custom end-useparts. Specifically, material extrusion 3D printing (also known as fusedfilament fabrication or fused deposition modeling), has emerged as atool of choice for direct consumer use, larger scale production, andquick thermoplastic prototyping as it is the easiest to operate,produces the least waste, and provides the shortest turnaround time ofconventional 3D printing technologies.

Many materials have been used to produce 3-D printed articles for a widevariety of end uses, from chocolate to collagen. Thermoplastic materialsare especially well adapted for use with 3-D printers. Unfortunately,there have been few thermoplastics available that provide high chemicalresistance, flame resistance, and good mechanical properties.

Some amorphous polymers like polyphenylsulfone (PPSU) have only a 3percent elongation when printed. Nylons have higher elongation (˜30%)but poor chemical resistance and must be dried prior to printing. Muchhigher elongation, flexible thermoplastic polyurethanes are availablebut have poor chemical resistance and weathering resistance.

Fluoropolymers are known for having excellent chemical resistance andgood mechanical integrity. Most fluoropolymers, such as fluorinatedethylene propylene (FEP), perfluoroalkoxy alkane (PFA), ethylenetetrafluoroethylene (ETFE), ethylene chloro-trifluoro ethylene (ECTFE),perfluoromethyl alkoxy polymer (MFA) have narrow processing windows(between Tm and degradation temp) that make 3D printing difficult. Inaddition they have high shrinkage on transition from the melt to a finalsolid, making warpage a real issue.

Polyvinylidene fluoride (PVDF) is a semi-crystalline fluoropolymer thatexhibits adhesion and warpage issues when 3-D printed. PVDF'ssemi-crystalline nature (PVDF homopolymer is known to have up to 50-65%crystallinity), and its high volume shrinkage during solidification(15-40%), lead to a high propensity to shrink and warp during filament3D printing. PVDF's low surface energy of generally 25 to 31 dyne-cmresults in poor adhesion to most materials.

Another issue facing fused deposition modeling printed plastics ingeneral is that due to the layer by layer deposition process, theprinted parts have significant mechanical anisotropy with propertiesmeasured in the z direction significantly lower than those measured inthe xy direction. The xy directions are parallel to the bottom buildstage, while the z direction is perpendicular to the build stage. Theprocess typically involves the deposition of a layer in the xy directionfollowed by another layer in the xy direction. The z direction is builtup by layers being deposited on top of each other. As a result printedfunctional parts do not perform as well in the z direction (such as aball joint snap fit printed vertically, as shown in the Examples).

There is a need for processes and/or formulations allowing foracceptable 3-D printing of crystalline fluoropolymer articles.Fluoropolymer articles are desirable in 3-D printing for their chemicalresistance, durability, flame resistance, and mechanical properties.Fluoropolymers such as PVDF that can be printed with little warpage andpart shrinkage are highly desired. Such materials could be used in theindustry for prototyping and custom end-use parts where high chemicalresistance, durability, and part integrity are needed.

Surprisingly, after much research, a semi-crystalline fluoropolymer andprocess conditions have now been developed, that can be used in afilament 3-D printing process with good resistance to shrinkage andwarpage. Additionally, the fluoropolymer or fluoropolymer formulationprovides high chemical resistance, high water resistance,hydrophobicity, thermal and UV resistance, high layer to layer adhesion,good use temperature, good mechanical properties, high Relative ThermalIndex (RTI) rating (130-150° C.), flame resistance, high elongation tobreak, and high impact, with the mechanical strength and stiffness thatvaries with the comonomer level in the PVDF, formulation components,filler type/level, and printing conditions. 3-D articles and partsprinted from these formulations and using the methods of the inventioncould be stiff or flexible, with improved print resolution, and approachthe strength and elongation to break of injection molded fluoropolymerparts. Filament made of the composition of the invention, due to itsexcellent moisture resistance, has a long shelf life of over a year,without any special moisture-resistant packaging.

Successful 3D printing of PVDF has been achieved by selection andadjustment of three parameters in the 3-D process, with excellentresults achieved by combining two or all three parameters. Theparameters include: polymer or polymer blend selection, optional fillerselection, and specific processing conditions.

SUMMARY OF THE INVENTION

The invention relates to a fluoropolymer composition for use in 3-Dprinting, wherein said fluoropolymer composition comprises afluoropolymer having a low shear rate viscosity of less than 13,000 Pa-sat its deposition temperature and 4 sec⁻¹, as measured by capillaryrheometry. For a polyvinylidene fluoride polymer or copolymer, the meltviscosity measurement temperature is 232° C.

In one embodiment the fluoropolymer composition has a high shear rateviscosity of 30 to 2000 Pa-s at 232° C. and 100 sec⁻¹, as measured bycapillary rheometry.

In one embodiment the fluoropolymer composition can be in the form of afilament or pellets. The composition can also contain from 0.01 to 50,preferably 0.1 to 40, and more preferably 1 to 30 weight percent of oneor more fillers, based on the weight of the fluoropolymer and filler.

In one embodiment the fluoropolymer composition is a blend of thefluoropolymer and up to 49 weight percent of one or more othercompatible, miscible, semi-compatible or semi-miscible polymers, whichcan be another fluoropolymer, a polymethyl methacrylate homopolymer orcopolymer, or a block copolymer with one or more compatible blocks andat least one incompatible block.

In a preferred embodiment, the fluoropolymer is a PVDF homopolymer, or aPVDF copolymer having at least 50 weight percent of VDF monomer units,and from less than 50 weight percent to 0.001 weight percent of one ormore comonomers selected from the group consisting oftetrafluoroethylene (TEE), trifluoroethylene (TrFE),chlorotrifluoroethylene (CTFE), dichlorodifluoroethylene,hexafluoropropene (HFP), vinyl fluoride (VF), hexafluoroisobutylene(HFIB), perfluorobutylethylene (PFBE), 1,2,3,3,3-pentafluoropropene,3,3,3-trifluoro-1-propene, 2-trifluoromethyl-3,3,3-trifluoropropene,3,3-tetrafluoropropene, 1-chloro-3,3,3-trifluoropropene, fluorinatedvinyl ethers including perfluormethyl ether (PMVE), perfluoroethylvinylether (PEVE), perfluoropropylvinyl ether (PPVE), perfluorobutylvinylether (PBVE), longer chain perfluorinated vinyl ethers, fluorinateddioxoles, partially- or per-fluorinated alpha olefins of C₄ and higher,partially- or per-fluorinated cyclic alkenes of C₃ and higher, andcombinations thereof.

In one embodiment, the fluoropolymer is a multiphase filament having atleast one polyvinylidene fluoride homopolymer or copolymer phase, and atleast one phase of another polymer, where the total of thepolyvinylidene fluoride homopolymer and copolymer phases makes upgreater than 50 weight percent of said filament.

In one embodiment the filler is selected from the group consisting ofcarbon fiber, milled carbon fiber, carbon powder, carbon nanotubes,glass beads, glass fibers, nano-silica, Aramid fiber, polyaryl etherketone particles or fibers, BaSO₄, talc, CaCO₃, graphene, nano-fibers,impact modifiers, and hollow spheres, and mixtures thereof.

The invention also relates to a process for forming a fluoropolymerarticle having low shrinkage and low warpage, using a 3D printer.

The invention also relates to three-dimensionally printed fluoropolymerarticles having a tensile strength at yield of greater than 70% of thetensile strength at yield of a fluoropolymer of the same compositionmade by injection molding, and/or an elongation at break of greater than50% of the elongation at break of a fluoropolymer of the samecomposition made by injection molding, and/or a stress at yield, ofgreater than 80% of the stress at yield of a fluoropolymer of the samecomposition made by injection molding.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1: Is a plot showing the angular shear behavior for severaldifferent PVDF samples.

FIG. 2: Pictures of gears printed by 3D printing using different PVDFmaterials. Left is PVDF 5, a carbon-filled PVDF, mid is PVDF 1, a PVDFpolymer with a mid-range viscosity, and right is PVDF 2, a PVDFcopolymer.

FIG. 3: Optical microscope images of PVDF 7 printed bars. Left is of105% flow, right is 120% flow. Left had gap ˜1.1 mm and right at 0.3 mm.The reduction in gap also correspond to increased part density andincreased strength.

FIG. 4: Picture of printed snap-fit socket laid on its side. Left isPVDF 5, middle is PVDF 1, and right is Nylon 618. The Nylon 618 socketbroke after one trial to fit in the ball. The PVDF 5 and PVDF 1 printedsockets survived multiple snap-fit tries. The PVDF 5 has print qualitycomparable to Nylon and other commercial materials.

FIG. 5: Shows parts form a comparative PVDF formulation after testing inthe warpage test. There is clear warping off of the base.

FIG. 6: Shows parts form a PVDF formulation of the invention aftertesting in the warpage test. Little or no warping off of the base isseen.

FIG. 7: Show the results of a comparative formulation (PVDF4) and aformulation of the invention (PVDF8) in the shrinkage test.

DETAILED DESCRIPTION OF THE INVENTION

The invention relates to 3-D printed fluoropolymer articles, and inparticular those made of polyvinylidene fluoride formulations, havinglow warpage, excellent chemical resistance, excellent water resistance,flame resistance, and good mechanical integrity. Good 3-D printablefluoropolymer formulations can be achieved by using select homopolymersor copolymers, selected formulations and fillers, selected processmethods, and combinations of these factors. In general, thecompositions, formulations, and processes of the invention reduce thelevel or effect of polymer crystallinity, which improves printproperties.

“Copolymer” is used to mean a polymer having two or more differentmonomer units. “Polymer” is used to mean both homopolymer andcopolymers. For example, as used herein, “PVDF” and “polyvinylidenefluoride” is used to connote both the homopolymer and copolymers, unlessspecifically noted otherwise. Polymers may be straight chain, branched,star, comb, block, or any other structure. The polymers may behomogeneous, heterogeneous, and may have a gradient distribution ofco-monomer units. All references cited are incorporated herein byreference. As used herein, unless otherwise described, percent shallmean weight percent. Molecular weight is a weight average molecularweight as measured by GPC. In cases where the polymer contains somecross-linking, and GPC cannot be applied due to an insoluble polymerfraction, soluble fraction/gel fraction or soluble fraction molecularweight after extraction from gel is used.

“Low shear viscosity”, as used herein is a measure of the melt viscosity(ASTM D3835-0) at a relatively low shear rate. This relates to theviscosity of the melt following printing. For purposes of thisinvention, the low shear rate at which viscosity is measured is at 4sec⁻¹. The actual shear rate of the fluoropolymer following printing isessentially zero. “High shear viscosity” as used herein is a measure ofthe melt viscosity at a relatively high shear rate. This relates to theviscosity of the melt as it moves through the nozzle on a 3-D printer.The high shear rate viscosity is measured herein as the melt viscosityat a shear of 100 sec⁻¹. It is desirable that the viscosity of the meltunder high shear is lower than the viscosity of the fluoropolymer meltunder low shear, as can be seen in FIG. 1, due to shear thinning.

“ASTM temperature for Melt Flow Testing”, as used herein is meant thatthe melt flow ranges of the fluoropolymers of the invention are testedat the temperature described in the corresponding ASTM method for themelt flow of that fluoropolymer. For example, for FEP this is ASTMD2116, for PFA it is ASTM D3307, for ETFE it is ASTM 3159, and for THVit is ASTM D1238, and for PVDF it is ASTM D3222. For blends and anypolymers not having a listed ASTM temperature for Melt Flow Testing,230° C. is used as the temperature for melt flow measurement.

Composition

Fluoropolymers useful in the invention include homopolymers orcopolymers containing fluorinated monomers. The presence of fluorine onthe polymer is known to impart enhanced chemical resistance, reducedcoefficient of friction, high thermal stability, and enhancement of thematerial's triboelectricity. The term “fluoromonomer” or the expression“fluorinated monomer” means a polymerizable alkene which contains in itsstructure at least one fluorine atom, fluoroalkyl group, or fluoroalkoxygroup whereby those groups are attached to the double bond of the alkenewhich undergoes polymerization. The term “fluoropolymer” means a polymerformed by the polymerization of at least one fluoromonomer, and it isinclusive of homopolymers and copolymers, and both thermoplastic andthermoset polymers. Thermoplastic polymers are capable of being formedinto useful pieces by the application of heat and pressure, such as isdone in 3-D printing. While thermoset fluoropolymers generally are notprocessed by 3-D printing, the precursors to, and oligomers of, thethermoset polymer could be printed, assuming the viscosity is adjustedto allow for a viscosity capable of being 3-D printed. Thickeners couldbe used to increase the viscosity of the pre-polymers, if needed, asknown in the art. Conversely, plasticizers or diluents could be added todecrease the viscosity of the pre-polymers. Once the pre-polymers are3-D printed together, they can then be cured (functionality reacted andcross-linked) using an appropriate energy source, such as heat, UVradiation, e-beam, or gamma radiation. One non-limiting example of athermoset fluoropolymer would be the use of vinylidene fluoride andhexafluoropropene monomers with a fluoromonomer having bromidefunctionality. The brominated fluoropolymer could be 3-D printed,followed by radical cross-linking through the bromine functionalityusing a pre-added thermal radical source, or one that generates radicalsupon application of light, UV, electron-beam, or gamma radiation.

The fluoropolymers may be synthesized by known means, including but notlimited to bulk, solution, suspension, emulsion, and inverse emulsionprocesses. Free-radical polymerization, as known in the art, isgenerally used for the polymerization of fluoromonomers.

Fluoromonomers useful in the practice of the invention include, forexample, vinylidene fluoride (VDF), tetrafluoroethylene (TFE),trifluoroethylene (TrFE), chlorotrifluoroethylene (CTFE),dichlorodifluoroethylene, hexafluoropropene (HFP), vinyl fluoride (VF),hexafluoroisobutylene (HFIB), perfluorobutylethylene (PFBE),1,2,3,3,3-pentafluoropropene, 3,3,3-trifluoro-1-propene,2-trifluoromethyl-3,3,3-trifluoropropene, 2,3,3,3-tetrafluoropropene,1-chloro-3,3,3-trifluoropropene, fluorinated vinyl ethers includingperfluoromethyl ether (PMVE), perfluoroethylvinyl ether (PEVE),perfluoropropylvinyl ether (PPVE), perfluorobutylvinyl ether (PBVE),longer chain perfluorinated vinyl ethers, fluorinated dioxoles,partially- or per-fluorinated alpha olefins of C₄ and higher, partially-or per-fluorinated cyclic alkenes of C₃ and higher, and combinationsthereof. Fluoropolymers useful in the practice of the present inventioninclude the products of polymerization of the fluoromonomers listedabove, for example, the homopolymer made by polymerizing vinylidenefluoride (VDF) by itself or the copolymer of VDF and HFP.

In one embodiment of the invention, it is preferred that all monomerunits be fluoromonomers, however, copolymers of fluoromonomers withnon-fluoromonomers are also contemplated by the invention. In the caseof a copolymer containing non-fluoromonomers, at least 60 percent byweight of the monomer units are fluoromonomers, preferably at least 70weight percent, more preferably at least 80 weight percent, and mostpreferably at least 90 weight percent are fluoromonomers. Usefulcomonomers include, but are not limited to, ethylene, propylene,styrenics, acrylates, methacrylates, (meth)acrylic acid and saltstherefrom, alpha-olefins of C4 to C16, butadiene, isoprene, vinylesters, vinyl ethers, non-fluorine-containing halogenated ethylenes,vinyl pyridines, and N-vinyl linear and cyclic amides. In oneembodiment, the fluoropolymer does not contain ethylene monomer units.

In a preferred embodiment, the fluoropolymer contains a majority byweight of vinylidene fluoride (VDF) monomer units, preferably at least65 weight percent VDF monomer units, and more preferably at least 75weight percent of VDF monomer units. Copolymers of VDF, and preferablycopolymers of VDF and HFP, are especially preferred. The comonomerreducing the level of crystallinity of the copolymer.

Other useful fluoropolymers include, but are not limited to,polychlorotrifluoroethylene (CTFE), fluorinated ethylene vinyl ether(FEVE), and (per)fluorinated ethylene-propylene (FEP).

Fluoropolymers and copolymers may be obtained using known methods ofsolution, emulsion, and suspension polymerization. In a preferredembodiment, the fluoropolymer is synthesized using emulsionpolymerization whereby the emulsifying agent (‘surfactant’) is eitherperfluorinated, fluorinated, or non-fluorinated. In one embodiment, afluorocopolymer is formed using a fluorosurfactant-free emulsionprocess. Examples of non-fluorinated (fluorosurfactant-free) surfactantsare described in U.S. Pat. Nos. 8,080,621, 8,124,699, 8,158,734, and8,338,518 all herein incorporated by reference. In the case of emulsionpolymerization utilizing a fluorinated or perfluorinated surfactant,some specific, but not limiting examples are the salts of the acidsdescribed in U.S. Pat. No. 2,559,752 of the formula X(CF₂)_(n)—COOM,wherein X is hydrogen or fluorine, M is an alkali metal, ammonium,substituted ammonium (e. g., alkylamine of 1 to 4 carbon atoms), orquaternary ammonium ion, and n is an integer from 6 to 20; sulfuric acidesters of polyfluoroalkanols of the formula X(CF—)₂—CH₂—OSO₃-M, where Xand M are as above; and salts of the acids of the formulaCF₃—(CF₂)_(n)—(CX₂)_(m)-SO₃M, where X and M are as above, n is aninteger from 3 to 7, and m is an integer from 0 to 2, such as inpotassium perfluorooctyl sulfonate. The use of a microemulsion ofperfluorinated polyether carboxylate in combination with neutralperfluoropolyether in vinylidene fluoride polymerization can be found inEP0816397A1. The surfactant charge is from 0.05% to 2% by weight on thetotal monomer weight used, and most preferably the surfactant charge isfrom 0.1% to 0.2% by weight.

The fluoropolymer of the invention can be defined by the low shear andhigh shear viscosity of the fluoropolymer at the temperature defined foreach fluoropolymer by the ASTM Melt flow Rate Testing Method.Preferably, the fluoropolymers of the invention have a low shear rateviscosity as measured at 4 sec⁻¹ of less than 13,000 Pa-s. by capillaryrheometry according to ASTM D3835, and more preferably of less than6,000 Pa-s at the temperature of melt deposition. Preferably the lowshear viscosity is greater than 250 Pa-s, more preferably greater than600 Pa-s, and more preferably greater than 1,000 pa-s. If the low shearviscosity is less than this, it is likely not to have a sufficient meltstrength for the production of filament. While not being bound by anyparticular theory, this low-shear viscosity range seems to allow theprinted polymer to stay where it is placed, and yet still be fluidenough for good interlayer adhesion and fusion. Higher low shearviscosity PVDF resulted in a higher level of warpage and shrinkage.Preferably the thermoplastic material has a high shear viscosity of 30to 2000 Pa-s, preferably 100 to 1700 Pa-s, more preferably 300 Pa-s to1200 Pa-s, at the temperature of melt deposition and 100 sec⁻¹. The keyviscosity behavior is a combination of both the viscosity of thematerial coming out of the nozzle, and how fluid the material stays atthe thermoplastic solidifies and crystallization occurs. In the case ofa polyvinylidene fluoride polymer or copolymer, the above melt viscosityranges are met when measured at 232° C.

Preferably the fluoropolymer or copolymer of the invention issemi-crystalline. While an amorphous polymer could work under theconditions described above, and not being bound to any particulartheory, it is believed that some level of crystallinity is useful for 3Dprinting as it improves interlayer adhesion, and there is a period oftime during the crystallization phase change for more chain entanglementbetween adjacent layers.

In one embodiment, the fluoropolymer of the invention could containreactive functional groups, either by using a functional monomer, or bya post-treatment. Once the functional polymer is processed into a usefularticle, it could then be reacted or cross-linked, such as by UVradiation, or e-beam, for increased integrity. Cross-linking is known inthe art to generally increase the tensile and flexural moduli, andreduce solubility and permeability of the cross-linked material, all ofwhich could be advantageous physical property enhancements depending onthe material's final application.

Blends of two or more different fluoropolymers are contemplated by theinvention, as well as blends of two or more fluoropolymers having thesame or similar monomer/comonomer composition, but different molecularweights.

Blends are also contemplated between fluoropolymer and compatible ormiscible non-fluoropolymers. In one embodiment, at least 50 weightpercent, more preferably at least 60 weight percent, and more preferablyat least 70 weight percent of PVDF with a polymethlmethacrylate (PMMA)homopolymer or copolymer. The PMMA copolymer of the alloy contains atleast 50 weight percent, and more preferably at least 75 weight percentof methylmethacrylate monomers units. The melt miscible blend of PVDFwith PMMA provides a surprising number of benefits including to reduceand control warpage, improve optical transparency when this isdesirable, reduce shrinkage, improve base adhesion, improve layer tolayer adhesion, and improve z direction mechanical properties. Inaddition the overall print quality is surprisingly improved. Low andvery low viscosity compatible or miscible non-fluoropolymers can also beused for improved printability.

The compatible non-fluoropolymer could be a block copolymer containingat least one miscible block. The immiscible block could confer otherproperties like enhanced impact, ductility, optical properties, andadhesive properties. Either block could contain functional groups. Inone embodiment, poly(meth)acrylate homo- and co-polymer blocks could beused as the compatible block in the block copolymer.

Blends of the fluoropolymer with other fluoropolymers or nonfluoropolymers can be accomplished by any practical means includingphysical blending of the different polymers as dry ingredients, in latexform, or in the melt. In one embodiment, filaments of two or morepolymers are coextruded in a core-sheath, islands in the sea, or otherphysical structure.

Blends of very low viscosity PVDF, homopolymer or copolymer, of 30 to1000 Pas at 100 s⁻¹ and 232° C., can be blended with a higher viscosityPVDF to improve interlayer fusion/adhesion. The overall blend will havean average melt viscosity within the range of the invention.

For example, it was found that blending a low viscosity PMMA polymer toa homopolymer PVDF improved its base adhesion, base warpage, shrinkage,and overall printability. Surprisingly, even a small amount ˜5% of PMMApolymer or copolymer added to the PVDF composition yielded a noticeableimprovement in base warpage and a 28% reduction in shrinkage and a ˜10%PMMA addition yielded further improvements in base warpage and a 37%reduction in shrinkage.

Similarly, adding a small amount (˜10%) of very low viscosity PVDFcopolymer also resulted in improved base adhesion and a 16% reduction inshrinkage even as the part became more elastomeric.

Throughout this application, PVDF and its blends and copolymers will beused as an exemplary fluoropolymer. It is understood that one skilled inthe art will understand that other fluoropolymers can be manipulated ina similar manner to provide similar benefits in 3-D printing.

Fillers

A second means found to provide good fluoropolymer filament for theproduction of 3-D printed articles involves the use of fillers blendedwith the fluoropolymer. While not being bound by any particular theory,it is believed that fillers serve to modify the crystallinity of thepolymer matrix. Lower crystallinity in the filled fluoropolymer blendcomposition leads to lower shrinkage. The melt to solid volume change isalso reduced by the use of fillers, further reducing shrinkage. Inaddition, fillers can improve tensile modulus to further reduce warpageand shrinkage.

Fillers can be added to a fluoropolymer by any practical means.Twin-screw melt compounding is one common method whereby fillers can beuniformly distributed into a fluoropolymer and the filled compositionpelletized. Fillers could also be dispersed into a fluoropolymeremulsion, with the blend being co-spray-dried, for a more intimate blendof the materials.

In one embodiment, the filler can be compounded into a PVDF-misciblepolymer (such as PMMA), and the filled miscible polymer then added tothe PVDF.

It was surprisingly found that when a PVDF homopolymer of the low shearmelt viscosity described above, was blended with about 20 weight percentof carbon powder, based on the volume of the PVDF/carbon blend, the 3-Dprinted parts produced had low warpage and shrinkage—and the printquality compares very well with commercially available 3D printingfilaments. This filled sample showed better 3D printing quality,including higher definition, than the unfilled homopolymer.

Surprisingly, the mechanical performance of 3D printed parts made withboth filled and non-filled fluoropolymer of the invention had enoughintegrity to produce strong snap fit components, while parts made ofcommercial polyamide filament cracked when fabricated into similar snapfit articles. For example, for a ball-joint snap fit part printed in thevertical direction, one printed from a commercial polyamide filamentbroke along the xy direction (z direction failure), whereas the partsprinted from carbon filled PVDF homopolymer filament did not. One couldexpect that a filled material would show a decrease in layer-to-layeradhesion, but no decrease of layer-to-layer adhesion was seen in thecarbon powder-filled PVDF.

Fillers can be added to the fluoropolymer at an effective level of from0.01 to 50 weight percent, preferably 0.1 to 40 and more preferably from1 to 30 volume percent, based on the total volume of the fluoropolymerand filler. The fillers can be in the form of powders, platelets, beads,and particles. Smaller materials, with low aspect ratios are preferred,to avoid possible fouling of the nozzle. Useful fillers for theinvention include, but are not limited to carbon fiber, carbon powder,milled carbon fiber, carbon nanotubes, glass beads, glass fibers,nano-silica, Aramid fiber, PVDF fiber, polyarylether ketone fibers,BaSO₄, talc, CaCO₃, graphene, nano-fibers (generally having an averagefiber length of from 100 to 150 nanometers), and hollow glass or ceramicspheres.

One could envision the use of particles with an aspect ratio designed toimprove mechanical strength as another alternative to the particulatefiller tested so far.

The addition of fillers was found to raise the melt viscosity of PVDF,however, provided that the PVDF composition as a whole was within thespecified melt viscosity parameters, the PVDF composition was printable.The addition of filler increased print quality and decreased warpage.

It is expected that the fillers, and especially fibers, can provideexcellent shrinkage reduction. One issue with fibers is that they tendto increase the viscosity of the melt, and could clog nozzles. Thiseffect could be minimized by using a lower melt viscosity fluoropolymer,a short aspect ratio fiber, or a larger nozzle size.

Other common additives may also be added to the fluoropolymercomposition in effective amounts, such as, but not limited to adhesionpromoters and plasticizers.

Process

The polymer or filled polymer formulation is formed into a filament,pellets, generally by an extrusion process, or is in the form of apowder, such as from an emulsion process.

Surprisingly the PVDF filament of the invention has a high, consistentbulk density, and little or no voids. Preferably less than 5 volumepercent, preferably less than 2 volume percent, more preferably lessthan 1 volume percent, more preferably less than 0.5 volume percent, andmost preferably less than 0.1 volume percent of voids are present in thefilament. The level of voids is dependent on many factors, such as themolecular weight, homopolymer or copolymer composition, filler andcompatible polymer percentage. Filament consistency is important, andfilament is generally fed to the printer based on length of thefilament.

Filament made of the composition of the invention can take severalforms. The filament could be mono-phase, or multi-phase. A multi-phasefilament could be formed with 2 or more concentric layers, to provide agood blend of properties. In one embodiment, an amorphous polymer formsthe outside layer, with one or more crystalline or semi-crystallinepolymers on the inside. In another embodiment, an inner and outer layercould have different levels of filler, compatible polymers, or both. Instill another embodiment, and islands-in-the-sea morphology could beproduced.

The compositions or resins will be 3D printed in a material extrusion(fused deposition modeling, fused filament fabrication) style 3D printerwith or without filaments (any size diameter, including 1.75 mm, 2.85 mmor other sizes) and with any sized nozzle at any speed that can usefilament, pellets, powder or other forms of the fluoropolymer rawmaterial. The 3-D printing of this invention is not a laser sinteringprocess. The fluoropolymer compositions could be made into filaments forsuch purposes. They could potentially be even sprayed-nozzled onto thesurface (sprayed melted plastic) to be printed, such as by ArburgFreeformer technology.

A general description of the printing process would involve thefollowing steps: Feeding the fluoropolymer filament, pellets or powderinto the 3D printer. The computer controls of the printer will be set toprovide a set volume flow of material, and to space the printed lines ata certain spacing. The machine will feed the fluoropolymer compositionto a heated nozzle at the set speed, the printer moving the nozzle intothe proper position for depositing the set amount of fluoropolymercomposition.

In a preferred embodiment, the polymer has a low shear melt viscosity asdescribed above. The printer would generally have a heated bed of50-150° C. (preferably above 90° C.).

In one preferred embodiment, the 3-D printer is programmed to operate ata 105 to 150% overflow. This means that the volume of fluoropolymercomposition fed by the printer is higher than the calculated volumerequired for the 3-D article being formed. The overflow packs thefluoropolymer closer together, helps to compensate for some shrinkage,while increasing the strength and mechanical properties of the printedarticle. The overflow can be set by two different means. In the firstmethod, the software is set to feed a higher percent of material intothe nozzle than would be normally needed. In the second method, thesoftware would be set to decrease the spacing between lines, and thuscreate an overlap in the lines, resulting in extra material beingprinted into the article.

Process parameters of the 3-D printer can be adjusted to minimizeshrinkage and warpage, and to produce 3-D printed parts having optimumstrength and elongation. The use of selected process parameters appliesto any extrusion/melt 3D printer, and preferably to filament printing.

One added advantage of PVDF over other materials is that it ishydrophobic, which means there is no need to dry the filaments beforeprinting, as with some polyamides and other materials, and no changesoccur in the filament during storage due to the hydrophobicity, UVstability, and chemical resistance. The filaments can be used as is inall environments.

In one embodiment, two or more nozzles, using two or more differentcompositions could be utilized to produce novel, larger, and lesswarping articles. One use would be to produce a less warping, rigid,better base adhering compatible or miscible material as the base, thenprinting the lesser adhering, higher shrinking desired material on top.A variant would be to use an acrylic base composition, followed by afluoropolymer composition on top.

Another variant utilizing just one nozzle, would be to place acompatible acrylic film on the heated bed as the base and then print thedesired fluoropolymer composition on top.

A unique embodiment of the invention, not possible in an injectionmolded part, is the formation of a mechanically asymmetric part madeusing a rigid and a flexible fluoropolymer whereby one direction (x)would be rigid and the other direction (y) would be flexible. This couldbe made by printing alternating bands of rigid and flexible material inone direction and only flexible in the other, perpendicular direction.The resulting mechanical properties, flex modulus and tensile modulus,of the part in one direction would be different than that in the otherdirection, making this part mechanically asymmetric. This design wouldbe enabled by the fluoropolymer's compatibility with each other evenacross a wide range of rigidity.

Properties

3-D articles produced from the polymer formulation, and under the proper3D printing conditions result in part flexibility and in some casesextremely high elongation at break. In one embodiment, a surprising highstrain to break was observed (˜700% compared to ˜6% for ABS and PLA and˜30% for a polyamide) when printed and tested in the xy direction,parallel to the build plate, while matching strain and stress to breakfor an injection molded part of a similar composition. Otherformulations showed excellent strain to break after 3D printing (70%elongation) compared to polymers commonly used, again in the xydirection. In another embodiment, an article formed from the polymerformulation of the invention showed greater than 50 percent, preferablyover 60 percent, and in some cases even over 80 percent of theelongation at break of a fluoropolymer part of the same composition madeby injection molding when printed and tested in the xy direction whilemaintaining over 75%, preferably over 85%, and in some cases over 95% ofthe stress at yield of the fluoropolymer part of the same compositionmade by injection molding. By combining all aspects of the inventiontogether—the selection of the proper viscosity, with the printingtechniques and with the use of fillers or polymer blends in the PVDF,even higher quality PVDF parts could be produced than with the purepolymer alone.

In one embodiment it was found that the 3-D printed fluoropolymerarticle had similar elongation and yield strength when printed andtested in the xy direction as an injection molded article of the samecomposition. These properties are unexpected for a 3-D printedfluoropolymer article, and indeed for any 3-D printed article of anypolymer chemistry or formulation.

In a preferred embodiment, an article was obtained having both greaterthan 700% elongation at break and also greater than 1500 psi stress atyield when printed and tested in the xy direction. In anotherembodiment, an article was obtained having greater than 70% strain atbreak and also greater than 3500 psi stress at yield when printed andtested in the xy direction. In still another embodiment, an article wasobtained having greater than 35% elongation at break and also greaterthan 6500 psi stress at yield when printed and tested in the xydirection. The elongation at break, strain at break, and stress at yieldseen in the xy direction with the composition of the invention are someof the highest available for any polymer chemistry or formulationcurrently available.

In another embodiment, it was surprisingly found that an article witheven small amount ˜5% of PMMA polymer or copolymer added to the PVDFcomposition, yielded improved layer adhesion and a 70% improvement inthe elongation at break of the article when printed and tested in the zdirection, while maintaining similar stress at yield. A 10% PMMAaddition yielded further improved layer adhesion and a 110% improvementin the elongation at break of the article when printed and tested in thez direction while still maintaining similar stress at yield.

Filament of the invention has excellent shelf life. The high moistureresistant fluoropolymer composition filament can be stored for month andeven years, with little or no moisture pick-up. No specialmoisture-resistant packaging is required, as is needed with other resinstypically used in 3-D printing like polylactic acid, and polyamides. Thefilament, and also articles formed from the filament of the inventionwill absorb less than 0.05% water, when placed in room temperature waterfor 24 hours. Adsorbed moisture in a filament leads to poor qualityprints.

Uses

The present invention provides the first non-hydgroscopic crystallineproduct for use in filament production and 3D printing for anengineering fluoropolymer resin.

3-D printed parts and articles are especially useful for articles to beused in harsh environments, in which chemical resistance, moistureresistance, UV resistance, flame resistance, and good mechanicalintegrity is required. The use of the parts or articles made with thecomposition and process of the invention are especially useful inchemical handling equipment, or for making parts to be exposed tochemical contact.

3-D printed fluoropolymer parts of the invention could find use in solarpanels, aircraft, and transportation, as well as other high performanceapplications. The 3-D printed parts have similar strength and elongationcompared to an injection molded part, and with the precision and detailthat can be obtained in a 3-D printing process. In addition, the 3-Dprinted parts of the invention display superior combined mechanicalproperty performances (stress at yield and elongation at break) comparedto currently available 3-D printed parts, such as those of polyamides,ABS and polylactic acid.

EXAMPLES

Materials:

PDVF 1: A PVDF homopolymer adhering to ASTM D3222 Type I, Grade 2, LowViscosity.

PVDF 2: A PVDF copolymer with a heterogeneous comonomer distribution inthe backbone chain containing 7-12% HFP by weight as a comonomer and amelting point of 160-168 C.

PVDF 3: A PVDF homopolymer adhering to ASTM D3222 Type I, Grade 2, LowViscosity.

PVDF 4 (comparative): A PVDF homopolymer having a high molecular weight,and a melt viscosity at 232° C. of greater than 10,000 Pa-s.

PVDF 5: A PVDF homopolymer with carbon filler at 15-25%.

PVDF 6: A PVDF random copolymer with a melting point of 155-160° C.

PVDF 7: A PVDF random copolymer with a melting point between 130 and138° C.

PVDF 8: A PVDF blend with PVDF homopolymer of low viscosity (PVDF 1)with a low viscosity PMMA added at 3-7 wt %.

PVDF 9: A PVDF blend with PVDF homopolymer of low viscosity (PVDF 1)with a low viscosity PMMA added at 8-12 wt %.

PVDF 10: A PVDF blend with PVDF homopolymer of low viscosity (PVDF 1)with a high flow PVDF random copolymer added at 9-12 wt %.

Warpage Test

A simple test was created to measure and compare base warpage of variousmaterials on the 3D printing build plate (base warpage being critical inthat if a part does not adhere to the base then the part cannot beprinted). A test to measure the shrinkage of the material can also bederived from this test.

The test involved printing thin lines/walls (of 0.8 mm thick, two pathsof the nozzle) of various lengths of different materials on a heatedglass plate (110 C) and looking to see which materials and at whatlengths the parts warped/came off the plate. The lengths tested werefrom 2 cm to 20 cm and a height of about 1 cm, with 3 lines of brim andusing polyvinyl acetate glue solution as mentioned in example 2.

Each print was then evaluated from the edges as either showing nowarpage, occasional warpage (some prints warping other times not), smallwarpage (any detachment from the base), medium warpage (a couple mm fromthe base), large warpage (>0.5 mm from the base), could not print (partcame off the base before it finished printing). The results are shown inTable 1. It was found that HFP-rich copolymers adhered better to thebase than PVDF homopolymers. As shown in FIG. 5, the PVDF 4(comparative) samples warp off of the base; while the PVDF 8 samples ofthe invention shown in FIG. 6 show little or no warpage.

Shrinkage Test:

A 4 cm long, thin line/wall (of 0.8 mm thick, two paths of the nozzle)was printed on a heated glass plate (110 C) with 3 brims around thesample to guarantee that the sample stays on the base. After printing,the distance edge to edge of the print at the most narrow was measuredand compare to the theoretical value (4.0 cm). This gives a % shrinkageand can relatively quantitatively compare the shrinkage acrossmaterials.

One can see the effect of viscosity and effect of blending with lowviscosity grade. From PVDF 4, to PVDF 1, to PVDF 3, dropping in lowshear viscosity, and also dropping in shrinkage. The introduction ofcompatible low viscosity blend, provides an additional drop inshrinkage. From PVDF 1, to PVDF 8, to PVDF 9. As seen in FIG. 7.

Example 1

A series of different PVDF formulations was evaluated for angular shearbehavior. The shear results are shown in FIG. 1.

Example 2

Filaments were produced using a Davis-Standard tubing line, followingsimilar procedures and set up as when they make welding rods (3 or 4 mm)rods—extruder, air/water cooler, and puller. These were produced on aDavis Standard 1.5 inch extruder with a 24:1 L/D with temperature setpoints at 350 F in the extruder, 335 F on the die and a line speed of 16to 18 fpm with the strand air cooled and fed into a 2 belt puller tocontrol the line speed.

The filaments were 3D printed on an Ultimaker 2 desktop fused depositionmodeling (fused filament fabrication, material extrusion) machine. Thedesign was manipulated and sliced by Cura, a standard 3D softwareprovided by Ultimaker. All ten of the PVDF samples produced filamentsand produced surprisingly good print quality articles with surprisingmechanical results (the one PVDF 4 with higher low shear viscosity than10,000 Pa-s being one showing large base warpage).

The mechanical test parts are printed solid with 0.8 mm walls, anddiagonal (45°) crisscross in-fill and 0.2 mm/layer thickness and nozzlediam. of 0.4 mm. Other sample parts are printed with various infill %,but also with 0.8 mm walls, diagonal (45°) crisscross in-fill and 0.2mm/layer thickness and nozzle diam. of 0.4 mm. Various % overflow (from0-20%) were also tested, being utilized to counter shrinkage. Generallymechanical properties increased with increasing % overflow up to ˜15-20%with the exact optimal overflow % depending on material/printparameters. Thus a 15-25% overflow is best for functional parts. Forprototype parts a 5-10% overflow could be used to get better printfinish.

The temperature of the nozzle was set at 260° C., build plate heated to110° C., print speed was 20 mm/s with 20% overflow, fan speed at 50%. Athin layer of polyvinyl acetate glue solution was used to help adhesionand for homopolymer PVDF filament a brim on the print was necessary. Thebuild plate is glass. Copolymers, while having a lower surface energyhave the surprising effect of having improved adhesion to the buildplate. Improved adhesion of the first layer to the build plate is a keyfactor in reducing warpage. The resulting printed parts are shown inFIG. 2.

Example 3: Printed Parts Mechanical Properties

Type IV tensile bars were printed in the XY direction (lying flat on thebuild plate) to test xy tensile properties. Optical images microscopyimages were taken of PVDF 7 tensile bars with increasing % overflow(from 5% to 20%). The results, optical and mechanical, show best filland properties with 20% overflow. Less shrinking resins would need lessoverflow. PVDF 5 for example needs only 10% overflow to reach optimalproperties and minimal gaps found on side walls. The optical microscopyimages are shown in FIG. 3.

Example 4

Mechanical results are listed below in Table 1 for the differentSamples. Printed PVDF 7 has extremely high elongation (˜700%) for anengineering material by 3D printing, and has an elongation and strengthmatching that of injection molded parts—which is extremely surprising in3D printing, and not known to be reported as of this writing for afluoropolymer or other 3D filament printing. PVDF 2 shows a drop inelongation of 3D printed part versus injection molded part (elongationis still high for 3D parts), but maintains ˜100% of the injection moldedtensile strength and compares very favorably to parts made withcommercial nylons (4600 psi stress at yield and 30% elongation). PVDF 6has the greatest tensile strength for the copolymer samples, withelongation as good as nylons (˜30%) but lower than other copolymers ofthis invention. Printed PVDF 1 has great balance of properties and underoptimal printing conditions the tensile strength and elongation to breakare 80-90% of that for an injection molded bar of PVDF 1. The overallmechanical strength of this grade is outstanding. Printed PVDF 5 whichhad very good printability and elongation similar to injection moldedPVDF, but only 60% of its stress at yield.

TABLE 1 Printed Printed Inject Stress at Strain at mold Yield InjectMold Materials % Break (%) Strain at [psi] Stress at Yield of interestOverflow in XY Break (%) in XY [psi] PVDF 7 15-25 733 670 1700 2100 PVDF2 20 72 530 4000 3850 PVDF 6 15 29.9 200 5400 5300 PVDF 1 15-20 41  60?7000 7500 PVDF 5 20 22  20 4150 4770 PVDF 5 10 22.5 ″ 4350 ″ PVDF 5  05.7 ″ 4050 ″ Nylon — 30 4600 ABS  5 5.9 20-30 4900 4940-7420 PLA  5 6 10 7500 8840-9500 psi

Example 5: Shrinkage

Shrinkage was measured on several Samples, using the shrinkage testdescribed above. The results are found in Table 2:

TABLE 2 MATERIAL length (mm) % shrinkage PVDF 3 38.60 3.5% PVDF 1 38.294.3% PVDF 4 37.62   6% PVDF 9 38.92 2.7% PVDF 8 38.75 3.1% PVDF 10 38.583.6%

Example 6: Z Direction Properties

Type 5BA ISO 527 tensile bars were printed in the Z direction(perpendicular to the build plate) to test Z direction tensileproperties and layer to layer adhesion. The parts are printed solid with0.8 mm walls, and diagonal (45°) crisscross in-fill and 0.2 mm/layerthickness and nozzle diam. of 0.4 mm. Z direction mechanical results arelisted below in Table 3, for the different samples. PVDF 8 and 9, whichhave some low viscosity PMMA blend into PVDF 1, show significantincrease in Z direction strain at break. With increasing yet still smallcontent of the compatible acrylate (3-7% and 8-12%), the Z directionstrain at break increases 70% and 110% respectively. PVDF 8 and 9demonstrate superior Z direction strain at break for a rigid materialcompared with other materials tested and commercially availablematerials with similar XY direction mechanical properties as PVDF 1.

TABLE 3 3D printed Z stress at yield 3D printed Z strain Name/Material(psi) at Break (%) PVDF 1 5500 5.1 PVDF 8 5600 8.9 PVDF 9 5500 10.9 PLACommercial 5500 1.4 Nylon 4100 5.4

Example 7

Generally PVDF homopolymers and PVDF copolymers defined in thisinvention yield parts that have very good interlayer strength whenprocessed according to this invention, which means properties closer tothat of injection molded products while retaining the outstandingchemical and flame resistance inherent in PVDF polymers. It also meansbetter layer to layer adhesion and better overall part performance.

A ball and socket model was printed out of Taulman 618 (a nyloncopolymer), PVDF 1, PVDF 5, and an acrylate using stereo lithography 3Dprinting (SLA) (FIG. 4). It was printed with 20% infill at 25 mm/s. Onlythe PVDF 1 and PVDF 5 ball and sockets could snap on and off even thoughtheir parts don't appear as nice. The sockets made from other materialsbroke upon inserting the ball. The Nylon 618 socket broke after onetrial to fit in the ball. The PVDF 5 and PVDF 1 printed sockets survivedmultiple snap-fit tries. The PVDF 5 has print quality comparable toNylon and other commercial materials, but the PVDF 1 is lacking bycomparison.

Within this specification embodiments have been described in a way whichenables a clear and concise specification to be written, but it isintended and will be appreciated that embodiments may be variouslycombined or separated without parting from the invention. For example,it will be appreciated that all preferred features described herein areapplicable to all aspects of the invention described herein.

Aspects of the invention include:

1. A fluoropolymer composition for use in 3-D printing, wherein saidfluoropolymer composition comprises a fluoropolymer having a low shearrate viscosity of less than 13,000 Pa-s at the temperature given in theASTM Melt Flow Testing for that fluoropolymer, and 4 sec⁻¹, as measuredby capillary rheomometry.2. The fluoropolymer composition for use in 3-D printing of aspect 1,wherein said fluoropolymer composition comprises a homopolymer ofvinylidene fluoride, or a copolymer comprising at least 65 weightpercent of vinylidene fluoride monomer units, and one or morecomonomers, having said low shear rate viscosity at 232° C. and 4 sec⁻¹of less than 13,000 Pa-s, as measured by capillary rheomometry.3. The fluoropolymer composition of any of aspects 1 or 2, wherein saidfluoropolymer has a high shear rate viscosity of 30 to 2000 Pa-s at 232°C. and 100 sec⁻¹, as measured by capillary rheomometry at thetemperature given in the ASTM Melt Flow Testing for that fluoropolymer.4. The fluoropolymer composition of any of aspects 1 to 3, wherein saidfluoropolymer composition is in the form of a filament or pellets.5. The fluoropolymer composition of any of aspects 1 to 4, wherein saidfluoropolymer composition further comprises from 0.01 to 50, preferably0.1 to 40, and more preferably 1 to 30 weight percent of one or morefillers, based on the weight of the fluoropolymer and filler.6. The fluoropolymer composition of any of aspects 1 to 5, wherein saidfluoropolymer composition comprises a blend of said fluoropolymer and upto 49 weight percent of one or more other compatible polymers.7. The fluoropolymer composition of any of aspects 1 to 6, wherein saidother compatible polymer is selected from a different fluoropolymer, apolymethyl methacrylate homopolymer or copolymer, or a block copolymerwith one or more compatible blocks and at least one incompatible block.8. The fluoropolymer composition of aspect 4, wherein said fluoropolymerfilament is a coextruded, multiphase filament having at least onepolyvinylidene fluoride homopolymer or copolymer phase, and at least onephase of another polymer, copolymer or blend, and wherein the total ofall polyvinylidene fluoride homopolymer and copolymer phases makes upgreater than 50 weight percent of said filament.9. The fluoropolymer composition of any of aspects 4 or 5, wherein saidfilament contains less than 5 volume percent of void space, preferablyless than 1 volume percent, and most preferably less than 0.5 volumepercent.10. The fluoropolymer composition of any of aspects 4 to 6, wherein saidfiller is selected from the group consisting of carbon fiber, milledcarbon fiber, carbon powder, carbon nanotubes, glass beads, glassfibers, nano-silica, Aramid fiber, polyaryl ether ketone fibers, BaSO₄,talc, CaCO₃, graphene, impact modifiers, nano-fibers, and hollowspheres, and mixtures thereof.11. The fluoropolymer composition of aspect 6, wherein blend comprisesat least two chemically different fluoropolymers, and/or fluoropolymersof differing weight average molecular weights wherein said weightaverage viscosity of the blend is <113000 Pa-s.12. The fluoropolymer composition of any of aspects 1 to 11, whereinsaid fluoropolymer is a PVDF homopolymer, or a PVDF copolymer having atleast 50 weight percent of VDF monomer units, and from less than 50weight percent to 0.001 weight percent of one or more comonomersselected from the group consisting of tetrafluoroethylene (TFE),trifluoroethylene (TrFE), chlorotrifluoroethylene (CTFE),dichlorodifluoroethylene, hexafluoropropene (HFP), vinyl fluoride (VF),hexafluoroisobutylene (HFIB), perfluorobutylethylene (PFBE),1,2,3,3,3-pentafluoropropene, 3,3,3-trifluoro-1-propene,2-trifluoromethyl-3,3,3-trifluoropropene, tetrafluoropropene,1-chloro-3,3,3-trifluoropropene, fluorinated vinyl ethers includingperfluoromethyl ether (PMVE), perfluoroethylvinyl ether (PEVE),perfluoropropylvinyl ether (PPVE), perfluorobutylvinyl ether (PBVE),longer chain perfluorinated vinyl ethers, fluorinated dioxoles,partially- or per-fluorinated alpha olefins of C₄ and higher, partially-or per-fluorinated cyclic alkenes of C₃ and higher, and combinationsthereof.13. A process for forming a 3-dimensional fluoropolymer article,comprising the steps of:

-   -   presetting the software of a 3D printer to a set volume flow and        line spacing for the printing of said article;    -   feeding the fluoropolymer composition of aspect 1 in the form of        filament, pellets or powder into the 3D printer;    -   feeding by the printer of the fluoropolymer composition melt to        one or more heated nozzles,    -   depositing the fluoropolymer composition melt at the set        location, line spacing and flow rate set by the software, to        form an article.        14. The process of aspect 13, wherein said flow rate and/or line        spacing represents an overflow of from 105 to 150 volume percent        15. A three-dimensionally printed fluoropolymer article, formed        of the fluoropolymer composition of any of aspects 1 to 12.        16. The three-dimensionally printed fluoropolymer article of        aspect 15, wherein said article has a tensile strength at yield,        of greater than 700% as measured in the xy direction.        17. The three-dimensionally printed fluoropolymer article of        aspects 15 or 16, wherein said article has an elongation at        break, of greater than 70 percent, and also greater than 1500        psi stress at yield when printed and tested in the xy direction.        18. The three-dimensionally printed fluoropolymer article of any        of aspects 15 to 17, wherein said article has a strain at break        of greater than 70 percent, and also greater than 3500 psi        stress at yield when printed and tested in the xy direction.        19. The three-dimensionally printed fluoropolymer article of any        of aspects 15 to 18, having a base material and on or more        different compatible polymer compositions on top of the base        layer, wherein said base layer is less warping and has better        adhesion to the support than the compatible polymer layer on top        of the base layer        20. The three-dimensionally printed fluoropolymer article of any        of aspects 15 to 19, wherein two or more fluoropolymers        compositions with different stress modulus, and two or more        nozzles are used, producing a mechanically asymmetric part made        using a rigid and a flexible fluoropolymer whereby one        direction (x) is rigid and the other direction (y) is flexible.        21. The three-dimensionally printed fluoropolymer article of any        of aspects 15 to 20, wherein said article is cross-linked after        printing by radiation.

What is claimed is:
 1. A process for forming a 3-dimensionalfluoropolymer article, comprising the steps of: a) presetting thesoftware of a 3D printer to a set volume flow and line spacing for theprinting of said article; b) feeding at least one fluoropolymercomposition in the form of filament, pellets or powder into the 3Dprinter; wherein the 3D printer heats the fluoropolymer composition toform a melt; c) depositing the melt through one or more nozzles at theset location, line spacing and flow rate set by the software, to form anarticle, wherein said fluoropolymer composition comprises afluoropolymer comprising either a homopolymer of vinylidene fluoride, ora copolymer comprising at least 65 weight percent of vinylidene fluoridemonomer units, and one or more comonomers, wherein said fluoropolymerhas a low shear rate viscosity at 232° C. and 4 sec⁻¹ of less than13,000 Pa-s, as measured by capillary rheomometry and a high shear rateviscosity of 30 to 2000 Pa-s at 232° C. and 100 sec⁻¹, as measured bycapillary rheomometry at the temperature given in the ASTM Melt FlowTesting for that fluoropolymer.
 2. The process of claim 1, wherein saidfluoropolymer composition is in the form of a filament or pellets. 3.The process of claim 2, wherein said filament is a coextruded,multiphase filament having at least one polyvinylidene fluoridehomopolymer or copolymer phase, and at least one phase of anotherpolymer, copolymer or blend, and wherein the total of all polyvinylidenefluoride homopolymer and copolymer phases makes up greater than 50weight percent of said filament.
 4. The process of claim 2, wherein saidfilament contains less than 5 volume percent of void space.
 5. Theprocess of claim 1, wherein said fluoropolymer composition furthercomprises from 0.01 to 50 weight percent filler based on the weight ofthe fluoropolymer and filler.
 6. The process of claim 5, wherein saidfiller is selected from the group consisting of carbon fiber, milledcarbon fiber, carbon powder, carbon nanotubes, glass beads, glassfibers, nano-silica, Aramid fiber, polyaryl ether ketone fibers, BaSO₄,talc, CaCO₃, graphene, impact modifiers, nano-fibers, and hollowspheres, and mixtures thereof.
 7. The process of claim 1, wherein saidfluoropolymer composition comprises a blend of said fluoropolymer and upto 49 weight percent of one or more other compatible polymers.
 8. Theprocess of claim 7, wherein said other compatible polymer is selectedfrom the group consisting of a different fluoropolymer, a polymethylmethacrylate homopolymer or copolymer, a block copolymer with one ormore compatible blocks and at least one incompatible block, andcombinations thereof.
 9. The process of claim 7, wherein blend comprisesat least two chemically different fluoropolymers, and/or fluoropolymersof differing weight average molecular weights wherein said weightaverage viscosity of the blend is less than 13000 Pa-s.
 10. The processof claim 1, wherein the one or more comonomers of the copolymer areselected from the group consisting of tetrafluoroethylene (TFE),trifluoroethylene (TrFE), chlorotrifluoroethylene (CTFE),dichlorodifluoroethylene, hexafluoropropene (HFP), vinyl fluoride (VF),hexafluoroisobutylene (HFIB), perfluorobutylethylene (PFBE),1,2,3,3,3-pentafluoropropene, 3,3,3-trifluoro-1-propene,2-trifluoromethyl-3,3,3-trifluoropropene, 2,3,3,3-tetrafluoropropene,1-chloro-3,3,3-trifluoropropene, fluorinated vinyl ether, fluorinateddioxoles, partially- or per-fluorinated alpha olefins of C₄ and higher,partially- or per-fluorinated cyclic alkenes of C₃ and higher, andcombinations thereof.
 11. The process of claim 10, wherein thefluorinated vinyl ether is selected from the group consisting ofperfluoromethyl ether (PMVE), perfluoroethylvinyl ether (PEVE),perfluoropropylvinyl ether (PPVE), perfluorobutylvinyl ether (PBVE) andcombinations thereof.
 12. The process of claim 1, wherein saidfluoropolymer has a low shear rate viscosity at 232° C. and 4 sec⁻¹ ofless than 10,000 Pa-s.
 13. The process of claim 1, wherein said flowrate and/or line spacing represents an overflow of from 105 to 150volume percent.
 14. The process of claim 1, further comprising the stepof cross-linking, by radiation, after step c).
 15. The process of claim14, wherein two or more fluoropolymers compositions with differentstress modulus are deposited.
 16. The process of claim 1, wherein two ormore nozzles are depositing the same or different fluoropolymercompositions.
 17. A three-dimensionally printed fluoropolymer article,formed by the process of claim 1.